It is conventional in industries involving the transportation or storage of abrasive materials, such as coal, various mineral ores, or other abrasives, to provide a steel substrate or liner for a wall or surface to be protected, and thereafter to weld specially prepared abrasion resistant ceramic tile or bricks to the backing. The surface to be protected may comprise by way of example the wall of a pipe or a chute exposed to abrasion, or surface portions of a military vehicle exposed to shrapnel or small arms fire.
Such bricks are commonly one inch thick fired silicon ceramic, such as an aluminum-silicon oxide or a silicon carbide compacted under high pressure from a dry powder and optionally with a suitable binder. The typical brick has four by six inch faces, although the dimensions may vary appreciably, say from one-half to two inches in thickness, with faces ranging from less than four inches in the shorter dimension to more than nine inches in the longer dimension. Also the brick may be molded from a molten abrasive resistant material such as basalt or an aluminumzirconium-silicate.
A common weldable brick is formed with a central welding hole about one inch in diameter that extends through an outer face of the brick and is constricted slightly adjacent to the opposite inner face to confine a weldable metallic insert. The latter is inserted into the larger or unrestricted opening of the welding hole and is retained adjacent to the restricted end by friction. With the welding insert arranged coaxially in the hole, the metal insert is welded to the steel backing or liner, either by conventional MIG (metal inert gas) welding or by conventional use of an arc welding rod. Thereafter the unrestricted opening of the welding hole is closed by insertion of a cylindrical closure plug.
In some instances, it is preferable to weld the metal insert by conventional arc welding to the steel backing or liner, but arc welding is not particularly convenient with the type of brick available heretofore because it is difficult to maintain the metal welding insert in a coaxial position at the reduced end of the hole. The welding insert is provided with a central opening through which a welding rod or wire must pass in order to contact the steel wall or backing. When the welding rod is extended through the aforesaid central opening in the welding insert, the latter is frequently knocked out of alignment by the rod and welded in a cocked position to the steel liner. A similar problem arises even during MIG welding when the MIG welding wire is inserted through the welding insert into contact with the steel backing or liner to which the brick is to be secured.
Not only will the resulting weld be less secure, but the cocked insert in some instances prevents the cylindrical closure plug from fitting flush with the outer surface of the brick. The plug will thus be subjected to excessive abrasion and will rapidly wear away. Furthermore, although the cylindrical plug is usually cemented within the welding hole, it frequently works loose even when it is flush with the outer surface of the brick, whereupon the metallic insert will rapidly wear away by the abrasive action and the entire brick will be dislodged.
Even if the metallic insert is properly located and welded to the steel backing, the cylindrical closure plug cannot extend axially within the welding hole to the extent desired because a certain amount of space must be allowed to accommodate the situation when the metallic insert is cocked out of its coaxial alignment within the hole. Accordingly, the wear resistant thickness of the brick at the region of the approximately one-inch diameter welding hole will be considerably less than the thickness of the adjacent portions of the brick. When the thinner cylindrical plug eventually abrades away, the metallic welding insert is rapidly disintegrated by abrasion at the exposed hole.
In addition, the one inch centrally located hole tends to weaken the brick across the diameter of the hole. In consequence, the comparatively brittle ceramic brick tends to break when subjected to impact during use, or when the installer of the brick attempts to break off a portion in order to provide a close fit near the edge of the wall to be lined. In that event, the brick tends to crack at the middle through the one inch hole instead of at the region where the craftsman's hammer strikes the brick.
An additional objection to bricks of the type described is that three loose pieces are required, i.e., the brick, the insert, and the cylindrical plug. The insert may be cemented in place, but the cementing involves an additional operation and increases the cost of the brick.
The above noted objections in regard to conventional ceramic or abrasion resistant bricks are magnified for bricks of less than an inch thick. Although many situations exist where weldable ceramic bricks, of say less than one-half inch thickness would be desirable, especially where the excessive weight of thicker bricks is a major problem, no such brick suitable for use in a wide range of applications has been available heretofore. Also solid bricks with no through hole are desirable for use in many applications, regardless of thickness. Such bricks are stronger, less subject to fracture by impact, and exhibit maximum wear life when subject to abrasion. However, attempts to secure solid bricks as an impact and abrasion resistant protection to a substrate have not been successful because of the imperviousness of the brick to the adhesive, usually an epoxy resin, the brittleness of the adhesive as it ages, and the extensive preparation of the substrate surface required for the cementing.